Installation manual

4.3.2. Content ltering in MTA Sendmail

The nod32sm module is a third-party program with the purpose to serve as a content lter for MTA Sendmail.

Using Sendmail’s Milter interface the nod32sm accesses all e-mail messages being processed by MTA Sendmail. In

order to enable ltering, enter the following lines into the [sm] section of main NOD32 conguration le.

agent_enabled = yes

sm_sock_path=“/var/run/nod32sm.sock“

In the next step, modify the ’/etc/mail/sendmail.cf’ le by entering the following specication into the section MAIL

FILTER DEFINITIONS:

Xnod32sm,S=local:/var/run/nod32sm.sock,F=T,T=S:2m;R:2m;E:5m

With these settings the MTA Sendmail will communicate with the nod32sm module via unix socket ’/var/run/

nod32sm.sock’. Flag F=T will result in temporary fail connection if the lter is unavailable. Flag T=S:2m denes

timeout 2 minutes for sending information from MTA to lter. Flag T=R:2m denes timeout 2 minutes for reading reply

from the lter. Flag T=E:5m means overall timeout 5 minutes between sending end-of-message to lter and waiting

for the nal acknowledgment.

Note that in case the timeouts for the nod32sm lter are set too small, the Sendmail can temporarily reject the

message which will attempt to pass through at a later time. This will lead to the continuous rejection of one and the

same message later. In order to avoid the problem, the timeouts have to be set properly. Thus one has to get into

account ’confMAX_MESSAGE_SIZE’ parameter dened in a sendmail.mc le that will provide not accepting messages

bigger than the appropriate parameter value (given in bytes). Taking into account this value and the maximum time

for processing of this amount of data by MTA (this can be measured) one can evaluate the appropriate timeouts for

nod32sm lter.

Finally, uncomment and modify the following line in the ’/etc/mail/sendmail.cf’ le.

OInputMailFilters=nod32sm

To reread the newly created NOD32 conguration, enter the following command.

/etc/init.d/nod32d reload

To accomplish the whole procedure, one has to restart the MTA Sendmail.

4.3.3. Content ltering in MTA Exim 3

Let’s look inside the exim conguration le ’/etc/exim/exim.conf’ (resp. in older versions ’/etc/exim.conf’) to become

familiar with its content. It is typically compound from the so called TRANSPORTS CONFIGURATION section, DIRECTORS

CONFIGURATION section and ROUTERS CONFIGURATION section. In order to congure exim to use our anti-virus you have

to dene special DIRECTORS CONFIGURATION entry:

#DIRECTORSCONFIGURATION

nod32_director:

driver=smartuser

condition=“${ifeq{$received_protocol}{virus-scanned}{0}{1}}“

transport = nod32_transport

verify = false

chapter 4 / Integration with E-mail Messaging System